(1) Field of the Invention
The invention is related to an aircraft with a fuselage that accommodates at least one air breathing propulsion engine, said fuselage being provided with an air intake through which an intake air stream is supplied to said at least one air breathing propulsion engine in operation, said aircraft comprising the features of claim 1.
(2) Description of Related Art
In aircraft with air breathing propulsion engines, such as gas turbine engines, gas propelled engines or diesel engines, a sufficient air supply to the air breathing propulsion engines must be ensured such that these engines are able to combust a provided air/fuel mixture properly in order to deliver a required amount of power to an underlying drive system. If, however, an intake air stream, which enters the air breathing propulsion engine, does not meet certain engine recommendations, e.g. pressure loss, temperature, swirl, distortion, etc., the engine may not perform sufficiently or as expected, especially regarding fuel consumption and exhaust emissions, which may be affected negatively. Accordingly, these engine recommendations must be considered when implementing an air intake for such an air breathing propulsion engine in an aircraft.
In cases, where the aircraft is implemented as a rotary-wing aircraft, e.g. as a helicopter, the integration of an air breathing propulsion engine into a fuselage of the helicopter inherently results in a performance degradation with respect to underlying performance specifications provided by the engine manufacturer, i.e. to corresponding performance losses. These performance losses due to the installation of the engine into the helicopter's fuselage, which are also referred to as “engine installation losses”, are generally divided into intake losses, exhaust losses and bleed air extraction losses, wherein intake losses are caused by total pressure drop, static temperature rise, swirl angle, pressure distortion, and so on.
However, as a helicopter fuselage generally exhibits limited space and volume, only a constrained air intake area can be realized. Additionally, the intake air stream for the air breathing propulsion engine must be directed from an ambient outside region of the helicopter fuselage into the engine plenum. Furthermore, the intake air stream must be cleaned, as it may be contaminated with foreign objects, such as dust, gravel, etc., which should ideally not be sucked into the engine, as they could damage the engine and thereby create additional efforts in order of costs, maintenance, and reliability.
Moreover, since the helicopter is adapted for multiple flight modes, i.e. hover, forward flight, backward flight, sideward flight, quartering, etc., the air breathing propulsion engine is provided with incoming air from various directions with differing pressures and temperatures. Therefore, usually two different types of air intakes are currently implemented on helicopters, which are respectively mainly designed for only one specific flight condition: so-called static intakes and dynamic intakes. These intakes are suitable to guarantee comparatively good engine output performances in the specific flight condition for which they are designed, while a lack in performance may occur for the other, or complementary, specific flight condition.
More specifically, a dynamic intake is an air intake that provides low pressure losses during forward flight conditions. Therefore, a dynamic intake usually implies some sort of scoop in order to provide sufficient high-pressure air to the engine plenum, so that dynamic pressure is introduced into the engine plenum.
The document EP 2 133 265 B1 describes such a dynamic intake of a helicopter. This dynamic intake is implemented as a dual air intake and comprises an outer air intake which ducts the intake air stream to a main engine of the helicopter, and an inner air intake ducting the intake air stream to auxiliary units, e.g. an oil cooler.
In contrast thereto, a static intake is an air intake with low installation losses during slow or hover flight conditions due to an unspoilt installation, which mainly does not provide high dynamic pressures, so that no or only a minimum of dynamic pressure is introduced into the engine plenum. Such static intakes are mainly used for helicopters and are usually provided with inlet barrier filters, knowing that these static intakes do no perform ideally in typical cruise flight conditions due to increased installation losses.
By way of example, the documents U.S. Pat. Nos. 8,163,050 B2, 6,595,742 B2, US 2009/0261208 A1 and U.S. Pat. No. 5,697,394 respectively describe such a static intake that is provided with an inlet barrier filter for removing contaminant from the intake air stream. According to U.S. Pat. No. 6,595,742 B2 and US 2009/0261208 A1, the inlet barrier filter is moveable between different associated operating positions and according to U.S. Pat. No. 5,697,394 a part of a fuselage cowling that is located upstream of the inlet barrier filter is moveable between such different associated operating positions.